The invention relates generally to radio frequency energy systems and more particularly to radio frequency energy repeaters and transponders.
As is known in the art, radio frequency energy repeaters and transponders have a wide variety of applications. One type of radio frequency energy repeater is a retro-directive repeater where a retro-directive antenna array in combination with other elements may be used, either with or without amplification, to return received electromagnetic energy to a transmitting source. For example, the well known "Van Atta" array, in which pairs of antenna elements are connected together by transmission lines of appropriate lengths, has an inherent ability to "retro-direct" received electromagnetic energy back to the source of such energy.
Another type of retro-directive system is described in U.S. Pat. No. 3,715,749, issued Feb. 6, 1973, entitled "Multi-Beam Radio Frequency System" inventor Donald H. Archer, and assigned to the same assignee as the present invention. Here, a pair of radio frequency multi-beam array antennas are connected together to provide a system which may operate in either an active mode or a passive mode, which may be operated selectively to respond to predetermined ones of spatially separated interrogating sources, and which may be equally and simultaneously responsive to interrogating signals from any one of a number of directions.